present invention relates to a fluid control apparatus, especially, a fluid control apparatus which communicates with an actuator, having a piston mounted therein capable of reciprocating movement by fluid pressure, with a fluid supply passage and a return passage.
The present invention is intended to provide a fluid control apparatus of the above-described type which has a blow down valve characteristic so that said piston is allowed to move only in one direction by an external force when supply of fluid to said actuator is stopped because at least one of said supply passage and said return passage is damaged.
The present invention is also intended to provide a fluid control apparatus of the above-described type which includes a manually operable mechanism by which the piston of the actuator can be moved by an external force, such as a manual force, regardless of supply of fluid when the members connected to the actuator or the actuator itself are serviced or checked.
As disclosed in U.S. Pat. No. 4,269,111, generally speaking, during flight, a spoiler of an airplane has a tendency to be pushed upwardly by lift generated by differential pressure between its upper and lower surfaces. Usually, an actuator, i.e., a fluid cylinder, is connected to the spoiler, and the spoiler is pressed downwardly by the fluid cylinder.
When the spoiler is required to be vertically moved, hydraulic pressure is supplied to the cylinder chambers.
When the hydraulic pressure source is damaged because of some reasons under a condition wherein the hydraulic pressure has been supplied to the actuator so as to lift the spoiler, it is necessary for the spoiler to be returned to a normal position by wind pressure acting on the spoiler or an external force acting on the spoiler due to flight attitude.
However, in a conventional apparatus, since one cylinder chamber of the actuator is not communicated with the other cylinder chamber, hydraulic oil exhausted from said one cylinder chamber is not supplied to said the other cylinder chamber. Accordingly, the other cylinder chamber will be supplied with hydraulic oil from a hydraulic pressure source.
When the hydraulic pressure source is damaged in such a conventional apparatus while the spoiler has been lifted, the spoiler is pressed by means of wind pressure acting on the spoiler which is caused by adjustment of the wind pressure acting on the spoiler or the flight attitude, and accordingly, the hydraulic oil is exhausted from the one cylinder chamber to which the spoiler is connected, and the piston is moved backwardly
Due to the backward movement of the piston, the other cylinder chamber sucks hydraulic oil. In this case, as described above, said one cylinder chamber is not communicated with said the other cylinder chamber, and therefore, hydraulic oil is sucked through a valve at a high speed. Consequently, there occurs cavitation in the sucked hydraulic oil or suction of external air through the damaged hydraulic pressure source.
Partial vacuums are formed in the hydraulic oil in the cylinder chamber of the actuator because of the above described cavitation or suction of air. Thus, the piston of the actuator cannot be held at a predetermined position because of existence of the vacuums. As a result, there is a problem that the spoiler connected to the actuator cannot be secured at a predetermined position.
Further, when maintenance and repairs, or inspection of the spoiler or the fluid cylinder is done in such a conventional apparatus, the spoiler or the piston of the actuator cannot be readily moved by manual operation because the hydraulic pressure in the cylinder, i.e., the actuator, is not released.